The use of elastomers as an additive to ashalts has been known to improve the properties of the asphalts. In asphalt roads, the addition of elastomers to the asphalt has shown the following advantages: improved stability under high temperatures, better flexibility at low temperatures, less cracking and crazing, no bleeding which results in better wet and dry skid resistance, better wear resistance, better resistance against stripping, better aging resistance, increased stability, better resistance to moisture penetration, more resilience, therefore, less long term creep, improves ductility, greater compressive strength, higher surface luminosity for better light reflection.
Because of their excellent aging qualities, elastomers made from ethylene and propylene such as the ethylene-propylene-diene random terpolymer referred to as EPDM, and the random ethylene-propylene copolymer referred to as EPM have been of particular interest as additives to asphalts. U.S. Pat. No. 3,669,918 discloses that when small amounts of an EPM copolymer are mixed with asphalt cement, the flexibility and impact strength of the asphalt cement are increased. U.S. Pat. No. 3,890,263 discloses that the viscosity of asphalt cement can be increased by the addition to the asphalt cement of a mixture of EPDM and polypropylene.
Unfortunately, EPDM and EPM elastomers are incompatible with typical asphalt cements and even after mixing thoroughly if allowed to stand at elevated temperatures, as is often required in practice, the elastomer will float to the surface of the asphalt cement and the advantages are lost.